Boat propulsion

Abstract

A safety shroud for attachment to the rear surface of the transom of an unmodified boat hull equipped with an inboard engine and a propeller tube and shaft rigidly fixed to the engine and extending with clearance through an enlarged opening in the transom, and a propeller on the shaft; the shroud being longitudinally and transversely downward concave to overlie the top and partly enclose the sides of the propeller, the shroud in longitudinal section being upwardly and rearwardly curved from the forward bottom edge of the shroud to just ahead of the propeller zone and then extending straight rearwardly. The lateral edges of the shroud extend generally upwardly and rearwardly from the forward bottom edge of the shroud to merge with the top rear edge thereof. Preferably the shroud is composed of inner and outer interconnected plastic shells, the outer shell having a downward concave reinforcing strut, closed at its bottom by the inner shell, and having a metal rudder support shaft therein. The shroud and boat together constitute a new and improved combination.

I claim: 
     
       1. A safety shroud for providing a propeller housing, mounting a rudder and controlling flow of water to the propeller, said shroud being adapted for mounting on the rear surface of a boat transom, said shroud comprising inner and outer shaped shells of substantially uniform wall thickness; said outer shell having an outwardly extending flange for attachment to the transom, a longitudinally extending hollow downwardly open reinforcing strut, and outwardly and downwardly curved edge portions; said inner shell having a curved downwardly concave transverse section and extending to the rear of said upper shell, the forward end of said inner shell being longitudinally rearwardly and upwardly curved from a position adjacent the bottom edge of the transom to overlie the propeller zone to cooperate with the transverse curvature to define a water guide channel effective to produce an upward flow of water in which a propeller is positioned for surface running the transverse vertical section of said inner shell at the propeller zone conforming generally to the propeller arc, the portion of the inner shell rearwardly from the propeller zone being of substantially uniform transverse cross-section and the portion of the inner shell between the propeller zone and its forward end having its bottom surface downwardly concave in both longitudinally and transverse vertical cross-section, said inner and outer shells being formed of reinforced plastic and permanently bonded together in zones of substantial area defined by identically shaped curved lateral edge portions. 
     
     
       2. A shroud as defined in claim 1, in which said inner shell closes the bottom open end of said strut to form a reinforcing box-section. 
     
     
       3. A shroud as defined in claim 2, in which said box-section mounts a substantially vertical rudder post. 
     
     
       4. A shroud for attachment to the rear surface of ransom of an inboard motor boat having a propeller shaft and shaft housing extending rearwardly with clearance through an enlarged opening in the transom, said shroud having a lower surface overlying and partly surrounding a propeller at the propeller zone to be occupied by the propeller and extending aft thereof, the portion of said shroud forwardly of the propeller zone having a smooth continuous uninterrupted bottom surface which is downwardly concave in both longitudinal and transverse vertical cross-sections, the portion of said shroud at the propeller zone having a bottom surface which in vertical transverse planes have a substantially acruate cross-section having a radius of curvature slightly greater than the radius of the arc described by the tips of propeller blades, the portion of the shroud at and rearwardly of the propeller zone having a lower surface of substantially uniform downwardly concave cross-section in vertical transverse planes, the lower surface of said shroud having a cross-section in its vertical central longitudinal plane which extends upwardly and rearwardly from a position adajacent the bottom of the shroud at its forward end in a smooth downwardly concave curve having a maximum curvature at its forward end which diminishes to substantially zero at the propeller zone, the lateral edges of the shroud extending upwardly and rearwardly from the bottom of the shroud at its forward end through points only slightly below the top of the circle defined by the tops of the propeller blades at the propeller zone, said shroud having a central longitudinally extending downwardly open hollow reinforcing rib extending for the full length thereof, a closure for the bottom of said rib forming a box-section therewith and pivot means for a rudder extending substantially vertically through said rib and closure at the rear end thereof.